Agricultural vehicles, in particular, such as tractors, combines, and trailers, as well as comparable vehicles, which are used on soft ground, are frequently equipped with large volume tires in order to achieve good terrain handling, good traction properties, and low ground pressure. Traction and ground pressure are especially low if low air pressure is set in the tires, so that in the field, operation with low tire pressure is preferred. However, with decreasing tire pressure, the carrying capacity of the tires decreases, and the rolling resistance and tire wear increases. Therefore, when traveling on hard ground, a high air pressure should be selected. To satisfy these contradictory requirements, tire-pressure regulating systems are used like those, for example, from DE 198 04 249 A1 or U.S. Pat. No. 5,647,927. With the aid of a tire-pressure regulating system, the tire air pressure can be adjusted optimally to the requirements of the corresponding use. The air pressure required for filling the tires in these tire-pressure regulating systems is provided by a compressor, which feeds an air pressure container.
From DE 101 11 532 A1, a tire-pressure regulating system is known in which the turbocharger of an internal combustion engine of a vehicle is used as a pressure source. In this way, previously typical storage containers can be eliminated, which is associated with considerable cost advantages. This tire-pressure regulating system is in the position to fill or to deflate the tires of a vehicle sufficiently quickly.
For quick tire filling, a sufficiently high air pressure of the compressed-air source is required, which, however, cannot be made available by the turbocharger without an additional load on the internal combustion engine, because the turbocharger generates too low a pressure, for example, in idle running of the internal combustion engine. A sufficient load of the internal combustion engine could be generated, for example, by a load of the on board hydraulic system or the drive mechanism. However, this, in turn, is difficult to realize because in such a case, the use of other tractor functions could be limited.